Large diameter optical waveguide splice

ABSTRACT

Techniques and systems suitable for performing low-loss fusion splicing of optical waveguide sections are provided. According to some embodiments, multiple laser beams (from one or more laser) may be utilized to uniformly heat a splice region including portions of the optical waveguide sections to be spliced, which may have different cross-sectional dimensions. According to some embodiments, the relative distance of the optical waveguide sections and/or the power of the multiple laser beams may be varied during splicing operations.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/755,708, filed on Jan. 12, 2004 now U.S. Pat. No. 8,070,369, whichclaims benefit of U.S. Provisional Patent Application Ser. Nos.60/439,106 and 60/439,243, both filed Jan. 10, 2003, which are hereinincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention relate to optical waveguideattachment techniques and, more particularly, to techniques forachieving a low loss large diameter fusion splice.

2. Description of the Related Art

Optical industry manufacturers have a variety of products that requireattachment or splicing to optical waveguide elements having a largerdiameter than typical optical fibers. For example, athermal gratings,gain flattening filters, pressure and temperature sensors, andpotentially many others type devices may be formed in large diameteroptical waveguides. In order to connect such devices to optical signalprocessing equipment, or other such devices connected in series, opticalfiber may be attached to the device. To facilitate attachment to suchdevices, the optical fiber may be encapsulated in a carrier or pigtailhaving a larger diameter.

Low-loss fusion splicing of optical fiber is a very common operation andmany techniques have been developed in order to facilitate this process.For example, one common technique is to use a laser to perform splices,as disclosed in “Optical fiber splicing with a low-power CO2 laser” byEgashira and Kobayashi, Appl. Opt. 16, 1636-1638 (1977), “Monomode fibrefusion splicing with CO2 laser” by Rivoallan et. al., ElectronicsLetters, vol. 19, No. 2, Jan. 20, 1983, pp 54-55, and U.S. Pat. No.5,161,207, entitled “Optical fiber circumferentially symmetric fusionsplicing and progressive fire polishing.”

Such conventional techniques, however, are typically limited to fiberdiameters of 400 um or less. Modifying devices utilizing thesetechniques to accommodate larger diameters optical waveguides (e.g., ofa large diameter carrier and device that may be greater than 1 mm) wouldpresent a challenge and may not be feasible, particularly when trying tomaintain uniform heating around the entire diameter of the splice areato achieve a strong splice, while also maintaining alignment of thenarrow (e.g., 5 um diameter) fiber cores to minimize optical lossthrough the splice region. As a result, encapsulated fiber pigtails areoften attached to large diameter devices via epoxy, which not onlylimits the heat, humidity, and corrosiveness of the environments inwhich the devices may be placed, but also results in optical loss if theepoxy is placed in the optical path.

Accordingly, what is needed is the capability to perform a largediameter splice (LDS), preferably using laser fusion thus reducing oreliminating many of the disadvantages associated with using epoxy.

SUMMARY OF THE INVENTION

The present invention generally provides methods and systems forperforming low loss fusion splicing of large diameter optical waveguidesections.

One embodiment provides a method for splicing two optical waveguidesections. The method generally includes aligning distal ends of the twooptical waveguide sections, fusing the distal ends of the opticalwaveguide sections by exposure to at least two separate laser beams, andmoving the distal ends of the optical waveguide sections relative toeach other during the fusing.

Another embodiment provides a method for splicing together two opticalwaveguide sections each having a diameter of at least 400 um. The methodgenerally includes a) aligning distal ends of the two optical waveguidesections, b) providing at least two laser beams for heating the opticalwaveguide sections, c) adjusting a power level of the at least two laserbeams, d) exposing the distal ends of the optical waveguide sections tothe at least two laser beams, and e) repeating steps c) and d) until thedistal ends are fully fused.

Another embodiment provides a system for fusing first and second opticalwaveguide sections together generally including at least one sourcelaser to provide at least one laser beam, first and second stages tohold the first and second optical waveguides, respectively, and a beamdelivery arrangement. At least one of the first and second stages ismovable to provide relative motion between the first and second opticalwaveguides while holding portions of the first and second opticalwaveguides to be fused within a fusion splice region. The beam deliveryarrangement delivers at least two laser beams to different locations ofthe fusion splice region, wherein the at least two laser beams aregenerated from the at least one laser beam provided by the at least onesource.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 illustrates an exemplary system for splicing optical waveguidesections in accordance with one embodiment of the present invention.

FIG. 2 is a flow diagram of exemplary operations for splicing opticalwaveguide sections in accordance with one embodiment of the presentinvention.

FIG. 3 is a relational view of optical waveguide sections to be splicedin accordance with one embodiment of the present invention.

FIG. 4 is a relational view that illustrates one technique for aligningoptical waveguide sections to be spliced in accordance with oneembodiment of the present invention.

FIG. 5 is a relational view that illustrates another technique foraligning optical waveguide sections to be spliced in accordance with oneembodiment of the present invention.

FIGS. 6A-6C illustrate optical waveguide sections at different stages ofsplicing process in accordance with one embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Embodiments of the present invention provide techniques and systems thatmay be used to perform low-loss fusion splicing of optical waveguidesections, with at least one of the optical waveguide sections having alarge diameter. According to some embodiments, laser fusion techniquesconventionally limited to small diameter optical waveguides (e.g.,conventional optical fibers) may be adapted to splice large diameteroptical waveguide sections. For example, while conventional laser fusiontechniques utilizing a single laser beam may provide insufficientheating uniformity for the larger splice region of such large diameteroptical waveguides, embodiments of the present invention may utilizemultiple laser beams (from one or more laser) to uniformly heat thelarger splice region, even if the waveguide sections to be spliced havedifferent cross-sectional dimensions.

As used herein, the term large diameter waveguide generally refers toany type waveguide having a larger diameter (or other cross-sectionaldimension if not round) than a conventional optical fiber, whichtypically has a diameter less than 400 um. For example, one type oflarge diameter waveguide that may be spliced is a sensor element havingone or more gratings formed therein, such as those described in U.S.patent application Ser. No. 09/455,868, entitled “Large Diameter OpticalWaveguide, Grating, and Laser”, filed Dec. 6, 1999, and herebyincorporated by reference. Such sensor elements are rigid structuresunlike optical fibers and have a core similar in size to that of aconventional optical fiber but may have an outer diameter of 3 mm ormore. Such large diameter optical waveguide sensor elements may beformed by using fiber drawing techniques now know or later developedthat provide the resultant desired dimensions for the core and the outerdimensions.

Alternatively, large diameter optical waveguides may be formed byheating, collapsing and fusing a glass capillary tube to a fiber by alaser, filament, flame, etc., as is described in co-pending U.S. Pat.No. 6,519,388 entitled “Tube-Encased Fiber Grating”, which isincorporated herein by reference. Alternatively, other techniques may beused to fuse a fiber to a tube, such as using a high temperature glasssolder, e.g., a silica solder (powder or solid), such that the fiber,the tube and the solder all become fused to each other, or using laserwelding/fusing or other fusing techniques.

FIG. 1 illustrates an exemplary system 100 for splicing opticalwaveguide sections 102 and 104 in accordance with one embodiment of thepresent invention. As previously described, one or both of the opticalwaveguide sections may have a larger diameter than conventional opticalfibers. For example, for some embodiments, one of the optical waveguidesections may be a large diameter sensor element, while the other opticalwaveguide section may be a large diameter carrier element used to attachto the large diameter sensor element. For one embodiment, one of theoptical waveguide sections may be a large diameter pigtail as describedin the commonly assigned co-pending application Ser. No. 10/755,722entitled “Low-Loss Large-Diameter Pigtail” filed herewith.

In the illustrated embodiment, the system 100 includes a holdingassembly 101 with stages (or fixtures) 103 and 105 for holding thewaveguide sections 102 and 104, respectively, within the path of one ormore beams 115 from a source laser 110 during a splice process. One orboth of the stages 103-105 may be movable in multiple directions (e.g.,along X, Y, and Z axes) to control relative position between and allowalignment of the sections 102-104 prior to and during splicingoperations, as will be described in further detail below. For someembodiments, the stage 103 may be mounted on a motor controlled lathe107 allowing rotation of the waveguide section 102. For suchembodiments, the stage 103 may include a tail stock (not shown) with abore through which excess fiber attached to the waveguide section 102may be routed. The lathe 107 may also include a port in the headstockthrough which vacuum (or a pressure gas such as nitrogen) may be appliedto the waveguide section 102.

The one or more beams 115 may be generated by splitting a single beam111 from the source laser 110, via one or more beam splitters 139.Directing multiple beams 115 to different locations about a spliceregion may provide more uniform heating than a single beam. Asillustrated, the split beams 115 may be focused and directed todifferent locations (e.g., separated by approx. 180° for two beams 115)about the splice region of the waveguide sections 102 and 104 by anarrangement of lenses 136 and mirrors 131. The exact size, type, andconfiguration of the lenses 136 and mirrors 131 will determine theactual size of the beams 115 and may be chosen according to the size andtype of the waveguide sections 102-104 to be spliced. For otherembodiments, rather generating multiple beams by splitting a beam from asingle source, beams from multiple laser sources may be directed to thesplice region.

In any case, the system 100 may also include a reference laser 112(e.g., a HeNe laser) that provides a beam 113 of visible light for useas a reference, for example, to assist in preliminary alignment of thewaveguide sections 102 and 104 (e.g., prior to turning on the laser110). For example, a camera 120 with a magnifying lens 121 may be usedto provide (to an operator) an image of the waveguide sections 102-104relative to a visible beam 113 on a monitor 122. As illustrated, thereference beam 113 may be provided by a combiner 137, split and travelthe same path as the source beam 111.

Various components of the system 100 may be controlled by a controller140 which may be implemented, for example, as a general purpose computersystem equipped with I/O interface cards and running appropriate controlsoftware (e.g., National Instrument's LabView). For example, thecontroller 140 may be configured to control relative movement betweenthe waveguide sections 102-104 before and during splicing operations(e.g., by controlling one or both of the stages 103-105) via one or morestepper motors (not shown). For some embodiments, the controller 140 maybe configured with an operator interface, for example, allowing anoperator to manually set laser power levels, control relative positionof waveguide sections 102-104, initiate automatic operations, and thelike.

As will be described in greater detail below, for some embodiments, thecontroller 140 may align the waveguide sections 102-104 while monitoringthe loss of optical power therethrough via an optical signal analyzer150. For example, during alignment operations, the optical signalanalyzer 150 may calculate the loss through the (unspliced) sections102-104 based on the power of a light signal from a broadband source 151transmitted through the waveguide section 102, received by the waveguidesection 104, and detected by a detector 152. To optimize alignment, thecontroller 140 (or an operator thereof) may iteratively move thewaveguide sections 102-104 to minimize such loss. After splicingoperations, the optical signal analyzer 150 may be used to measure theoptical power loss through the completed splice.

The controller 140 may also be configured to adjust power of the laser110 during splicing operations (automatically or based on operatorinput), as well as during pre/post-splicing operations, such aspolishing and annealing. For some embodiments, the controller 140 maymonitor the actual output power of the laser 110 via a detector 141 anda laser power meter 142, thus providing a feedback loop and allowing forprecise laser power adjustments. As illustrated, the detector 141 maydetect a small portion of the laser beam 111, such as the weak side ofan unbalanced beam splitter 132 (e.g., the 10% side of a 90/10 beamsplitter). The controller 140 may also be configured to control exposureof the waveguide sections 102-104 to the beams 115 via a beam stopassembly 133, illustratively including a shutter 134 and shutter control135. For some embodiments, the controller 140 may be configured tocontrol splice operations by exposing the waveguide sections 102-104 ateach power level for corresponding predetermined amounts of time, withthe exact times and power levels determined, for example, based on theexact dimensions and materials of the optical waveguide sections102-104.

FIG. 2 is a flow diagram of exemplary operations 200 for splicingoptical waveguide sections in accordance with one embodiment of thepresent invention. The operations 200 may be performed by components ofthe system 100. Thus, the operations 200 may be described with referenceto FIG. 1, as well as FIGS. 3-6 which illustrate waveguide sections102-104 at various stages of splice processing, according to variousembodiments.

The operations 200 begin, at step 202, by preparing ends of largediameter optical waveguide sections to be spliced. The optical waveguidesections to be spliced, whether they are large diameter collapsedpigtails, such as those described in co-pending commonly owned U.S.Patent Application 60/439,106, cane type waveguide structures, or othertype waveguide structures, may be first cut and polished on ends to befused. As illustrated in FIG. 3, each section 102-104 may be cut flatacross a cross-section and ends 302-304 may be polished to achieve aslight curvature. The curvature of the ends 302-304 may allow cores 306of the waveguide sections 102-104 to be aligned and prevent thepossibility of trapping air therebetween during fusion. If the curvatureis not present, the ends 302-304 must be more closely matched with aflat polish, which may complicate alignment. In any case, polished ends302-304 may be cleaned, for example, with an acetone wipe, followed by amethanol wipe and may further be blown with clean air before fusing.

At step 204, the waveguide sections are aligned and, at step 206, one ormore reference measurements of optical loss through the waveguidesections before splicing are taken. For example, the sections 102-104may be mounted in their corresponding stages 103-105, configured toallow X, Y, Z, and angular alignment. For some embodiments, the stages103-105 may be angularly aligned to each other in an effort to reduce oreliminate the amount of angular adjustment required. As illustrated inFIG. 3, for some embodiments, ends 302-304 of the waveguide sections102-104 may be heat cleaned (or “fire-polished”) by bringing them intothe beams 115, for example, with the laser 110 set at a lower powerlevel than that used for fusion. After such polishing, the laser isturned off and the parts are allowed to cool before alignment.

In some cases, reference measurements may be taken through eachwaveguide section 102-104 individually, and used to estimate lossthrough the sections 102-104 together. As previously described, for someembodiments, optical loss measurements through the waveguide sections102-104 to be spliced may be taken during alignment operations. Forexample, these measurements may be compared against the referencemeasurements or estimated loss to determine when the sections 102-104are adequately aligned.

As illustrated in FIG. 4, in some cases, optical loss measurements maybe taken by connecting one waveguide section to be fused (e.g., section104) to a source 151 and connecting the other waveguide section (e.g.,section 102) to a detector 152. The optical power loss through thesections 102-104 may be minimized (throughput power maximized) to ensurethe best alignment. As illustrated in FIG. 5, an alternative alignmentmethod utilizes one or more gratings 502 written into a fiber connectedto one of the waveguide sections (e.g., section 102) to be spliced. Inthis case, the section to be spliced without the grating 502 (e.g.,section 104) is connected to a source 151 and optical signal analyzer150, and the grating reflectivity is monitored. Maximizing the gratingreflectivity indicated by measurements from the analyzer 150 ensuresoptimal alignment of the waveguide sections 102-104 (due to theround-trip path, the difference between the expected and measuredreflectivity corresponds to twice the loss across the waveguide sections102-104). Either of these methods can also be used to provide anestimate of the splice loss (by comparing the throughput optical poweror grating reflectivity) before the splice (e.g., with butt-coupledsections 102-104) with that measured after the splice is complete.

Once aligned, the waveguide sections 102-104 are fused together bycontrolled exposure to the beams 115 generated from the one or moresource lasers 110. At step 208, the laser power is adjusted (orinitially set). At step 210, the waveguide sections are brought together(e.g., until they are butt-coupled, as illustrated in FIG. 6A). At step212, in an (optional) effort to reduce or eliminate bulging at thesplice region, as waveguide material around the splice region begins tomelt and flow around the ends 302-304, the waveguide sections 102-104are pulled apart slightly (as illustrated in FIG. 6B). The change inrelative distance between the waveguide sections 102-104 during thispushing and pulling may vary with the diameter of the waveguide sections102-104 and the relative distance may be changed at a relatively lowrate (e.g., approx. 50 um/sec).

As illustrated, the operations 208-212 may be repeated until the spliceis complete (as determined at step 214). For some embodiments, the laserpower may be increased incrementally (e.g., by 1-5% each pass), and thewaveguide sections 102-104 may be exposed for a given time (e.g., agiven number N seconds each pass). FIG. 6C illustrates a completedsplice having a fused regions 602. Completion of the splice may beindicated when a heat zone (e.g. monitored via a camera) is visiblethroughout the entire fused region 602.

At step 216, once the splice is complete, the laser power is broughtdown (reduced). For some embodiments, the laser power may be broughtdown slowly to allow for annealing of the splice region 602. In anycase, after the parts have cooled, at step 218, the optical loss throughthe (completed) splice is measured (e.g., by measuring throughput powerand/or grating reflectivity) and compared to the (pre-splice) referencemeasurement taken at step 206 to obtain an estimate of the loss acrossthe splice. Recall if grating reflectivity is measured, the differencebetween the two readings represents twice the splice loss since thelight path has to go through the splice area twice. While these lossmeasurements may provide reasonable estimates, more reliable cutbackmeasurements may also be made to obtain more accurate splice lossmeasurements.

The techniques described herein provide methods and techniques that aresuitable for laser fusion splicing large diameter (e.g., >1 mm) opticalwaveguides with low loss across the spliced regions. The uniform heatingof splice regions attainable through the use of multiple beams may allowfor a stronger splice joint without the use of epoxy, thus reducing oreliminating the temperature and humidity constraints associated withepoxy. Further, eliminating epoxy from the optical path may reducesplice loss. For some embodiments, utilizing the techniques describedherein, the loss across a large diameter splice may be less than 0.25dB.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

The invention claimed is:
 1. A method for splicing together two opticalwaveguide sections, wherein at least one of the optical waveguidesections comprises a core disposed in at least one cladding, the methodcomprising: a) aligning distal ends of the two optical waveguidesections, wherein a cross-sectional dimension of the at least one of theoptical waveguide sections is greater than 400 μm; b) providing at leasttwo laser beams for heating the optical waveguide sections; c) adjustinga power level of the at least two laser beams; and d) exposing thedistal ends of the optical waveguide sections to the at least two laserbeams.
 2. The method of claim 1, wherein the two optical waveguidesections have different cross-sectional dimensions.
 3. The method ofclaim 1, further comprising repeating steps c) and d) until the distalends are fully fused.
 4. The method of claim 3, further comprisingdetermining the distal ends are fully fused by monitoring a heat zoneincluding coupled portions of the two distal ends.
 5. The method ofclaim 1, wherein providing at least two laser beams for heating theoptical waveguide sections comprises splitting a beam from a singlesource laser.
 6. The method of claim 1, wherein exposing the distal endsof the optical waveguide sections to the at least two laser beamscomprises operating a shutter device.
 7. The method of claim 1, furthercomprising taking a measurement of optical power through the distal endsfor use in calculating optical loss therethrough.
 8. A method forsplicing two optical waveguide sections, comprising: aligning distalends of the two optical waveguide sections, wherein at least one of theoptical waveguide sections comprises a large diameter optical waveguidehaving a core disposed in at least one cladding and wherein an outerdiameter of the large diameter optical waveguide is greater than 400 μm;and fusing the distal ends of the optical waveguide sections by exposureto at least two separate laser beams.
 9. The method of claim 8, whereinthe two optical waveguide sections have at least one differentcross-sectional dimension.
 10. The method of claim 8, further comprisingmoving the distal ends of the optical waveguide sections relative toeach other during the fusing.
 11. The method of claim 8, whereinaligning the distal ends of the optical waveguide sections comprises:taking a measurement of optical power transmitted through a coupling ofthe distal ends of the optical waveguide sections.
 12. The method ofclaim 11, wherein taking a measurement of optical power transmittedthrough the coupling of the distal ends of the optical waveguidesections comprises: transmitting light through one of the opticalwaveguide sections; and measuring the optical power of light reflectedfrom one or more gratings in the other optical waveguide section. 13.The method of claim 8, further comprising generating the at least twoseparate laser beams from a single laser beam.
 14. The method of claim8, wherein fusing the distal ends of the optical waveguide sectionscomprises varying the power of the at least two separate laser beamsduring the fusing.
 15. The method of claim 8, wherein fusing the distalends of the optical waveguide sections comprises operating a shutterdevice to intermittently expose the distal ends to the at least twoseparate laser beams.
 16. The method of claim 10, wherein moving thedistal ends of the optical waveguide sections relative to each otherduring the fusing comprises: moving at least one distal end closer tothe other distal end during one portion of the fusing; and moving the atleast one distal end away from the other distal end during anotherportion of the fusing.
 17. The method of claim 8, further comprisingpolishing the distal ends of the optical waveguide sections prior to thefusing by: setting the power of the at least two separate laser beams toa level lower than that used during the fusing; and exposing the distalends to the at least two separate laser beams at the lower power level.18. The method of claim 8, further comprising providing a curvature onthe distal ends of the optical waveguide sections.
 19. The method ofclaim 8, wherein dimensions of the at least two separate laser beams areselected to provide uniform heating to distal ends of the opticalwaveguide sections having outer diameters greater than 400 μm.
 20. Themethod of claim 10, wherein moving the distal ends of the opticalwaveguide sections relative to each other during the fusing comprisesmoving stages that hold the optical waveguide sections relative to eachother during the fusing.